1. Field of the Invention
The invention relates to the field of rotary position encoders for electronic instruments, and more specifically, to rotary position encoders of the type having a shaft-retracted position for storage and a shaft-extended position for adjustment.
2. Related Art
Position encoders are used in a variety of applications for electronic instruments. A position encoder converts a rotary motion caused by a user turning a knob to a varying electrical signal which can be used to adjust an operational parameter of an electronic instrument. For example, a position encoder may be used to adjust the volume in an automobile audio system.
In one type of rotary position encoder, the encoder shaft is movable longitudinally or axially between a retracted position and an extended position. In the retracted position, the encoder shaft may be stored such that it extends only slightly from the front panel of an instrument. In the extended position, the shaft moves longitudinally out from the panel for ease of adjustment.
A spring loaded toggle system allows the shaft to move between the two positions by simply depressing the end of the shaft. The capability of providing both rotary and longitudinal movement is achieved by keying the shape of the shaft and the rotor plate within the encoder so that the rotor will turn with the shaft while permitting the shaft to move freely through the rotor in an axial or longitudinal direction.
In order to accommodate both rotary coupling and longitudinal movement while accounting for manufacturing tolerances, a minimum amount of "clearance" or imprecision must be present between the size of the keyed opening in the rotor and the size of the keyed shaft. This imprecision results in what is known in the industry as "backlash" in the rotary coupling between the shaft and the rotor. This is undesirable in most applications either because of the need for positional accuracy or the perceived lack of quality in the tactile feel of the device.